The present invention relates to a gas-liquid separation device of an internal combustion engine, and more particularly relates to a gas-liquid separation device disposed in a blow-by gas return passage of an internal combustion engine used in outboard motors.
In four cycle internal combustion engines used in outboard motors (or outboard marine engines), it has been known to provide a bore in the cylinder head and cylinder block to form a crankcase ventilation passage (or breather passage) for bringing the crankcase into flow communication with the valve operating cam chamber defined in the cylinder head to thereby control the pressure pulsation in the crankcase caused by reciprocating movements of the pistons. In such a configuration, the gases passing through the gap between the piston ring and the cylinder wall into the crankcase (i.e., blow-by gases) are circulated back to the intake passage via the crankcase ventilation passage and the valve operating cam chamber due to the negative pressure produced in the intake passage so that the blow-by gases, which may contain unburned components, are not emitted into the atmosphere.
Also, a gas-liquid separation chamber is preferably defined in the cylinder head cover or the like between the intake passage and the valve operating cam chamber in order to prevent the oil mist contained in the blow-by gases from mixing with the intake air. The blow-by gases entrained with the oil mist enter the gas-liquid separation chamber through an inlet port, and as the blow-by gases flow through a tortuous passage defined in the gas-liquid separation chamber, the oil contained in the blow-by gases is liquefied and separated from the gases. The separated oil is discharged from the gas-liquid separation chamber through an outlet port back to the valve operating cam chamber (see for example Japanese Patent Application Laid-Open (Kokai) No. 8-21226).
The inlet and outlet ports may be preferably provided with reed valve members to form one-way valves that open and close in response to a pressure difference between the valve operating cam chamber (or crankcase) and the gas-liquid separation chamber (or intake passage).
In such a gas-liquid separation device comprising the reed valves, however, when the reed valve member associated with the outlet port operates to abut a wall surface around the outlet port to close the same, the reed valve member tends to force the lubricating oil that has accumulated in an inside of the outlet port back into the gas-liquid separation chamber. Such a xe2x80x9cpumping effectxe2x80x9d caused by the valve-closing action of the reed valve member can undesirably decrease the return efficiency of the separated lubricating oil to the valve operating cam chamber.
In view of such problems of the prior art and the recognition by the inventors, a primary object of the present invention is to provide an improved gas-liquid separation device for an internal combustion engine that can ensure a smooth discharge of the liquefied lubricating oil from the gas-liquid separation chamber.
A second object of the present invention is to provide such an improved gas-liquid separation device suitable for an internal combustion engine used in an outboard motor.
A third object of the present invention is to provide such an improved gas-liquid separation device without a substantial increase in the number of component parts and manufacturing cost.
According to the present invention, these and other objects can be accomplished by providing a gas-liquid separation device for an internal combustion engine, comprising: a gas-liquid separation chamber defined in a part of the engine, the chamber being provided with first and second ports communicating with a crankcase, and a third port communicating with an intake passage, the first port being provided with a first one-way valve for allowing blow-by gas from the crankcase to flow into the chamber, and the second port being provided with a second one-way valve for allowing oil separated from the blow-by gas to be discharged from the chamber, wherein the second one-way valve includes a reed valve member adapted to selectively close the second port, and a valve seat defined by an annular surface which is elevated from a surface of a wall surrounding the second port and defines a larger opening area than the second port.
In this way, due to the elevated valve seat having a larger opening area than the second (oil discharge) port, a space having a certain volume is defined in the valve-closing state between the reed valve member and the wall surface around the second port. This space effectively serves to dampen or reduce the xe2x80x9cpumping effectxe2x80x9d caused by the closing action of the reed valve, thus preventing the oil accumulated in the second port from being pushed back to the inside of the gas-liquid separation chamber to thereby ensure a smooth discharge of the separated lubricating oil from the gas-liquid separation chamber.
In a preferred embodiment, said annular surface comprises a free end of an annular protrusion extending out from the wall surface surrounding the second port. Such a configuration may be preferable in view of easily providing the elevated annular surface serving as a valve seat. It will be further preferable if the wall comprises an elevated surface substantially aligned with the valve seat, and a base portion of the reed valve member is secured to the elevated surface. This can ensure a preferable contact between the reed valve member and the valve seat.
Typically, the internal combustion engine comprises: a cylinder head defining therein a valve operating cam chamber communicating with the crankcase; and a cylinder head cover attached to the cylinder head to cover the valve operating cam chamber, the cylinder head cover comprising a rib-like wall defining a concave cavity in the cylinder head cover so that an opening side of the concave cavity faces the valve operating cam chamber, wherein a plate member is attached to a free end of the rib-like wall to close the concave cavity to thereby define the gas-liquid separation chamber. The second port can be conveniently formed in the plate member. Such a configuration can provide a compact and easily assembled gas-liquid separation device.
The plate member may preferably extend substantially vertically in an operating state of the internal combustion engine, in that the second port is provided in a lower part of said plate member and said reed valve member is adapted such that its lower portion can flexibly move to be detached from/contact the valve seat. Such a configuration can desirably facilitate accumulation of the oil separated from the blow-by gases in the gas-liquid separation chamber as well as discharge of the accumulated oil from the gas-liquid separation chamber.
The gas-liquid separation device having above configurations may be particularly suitable for a vertical-crankshaft type engine typically used in outboard motors.
Other and further objects, features and advantages of the invention will appear more fully from the following description.